1. Field of the Invention
The invention relates to a miniaturized circuit housing for encapsulating and providing external contacts for integrated circuits and, in particular, a housing with a housing floor and an oppositely disposed housing lid which presses a circuit contact element positioned therebetween resiliently against the upper surface of the housing floor.
2. Description of the Related Art
Integrated circuits (chips) employed in electronic devices are almost always mounted in housings. These housings protect the sensitive semiconductor structures from harmful environmental influences such as moisture, light, dust and mechanical forces. In many cases enclosure in a housing simultaneously serves to adapt the structural widths and distances customary in LSI and VLSI technology to the—sometimes substantially larger—structural dimensions of printed circuits.
The physical properties of their housings influence the electrical behaviour and the reliability of chips to a considerable degree, and the technique of constructing housings and installing circuits in them is a substantial aspect of the overall process of manufacturing semiconductor components, which contributes appreciably to the final performance parameters and costs.
During the development of semiconductor technology, different types of housing were designed, with countless variants. From the viewpoint of mounting on a circuit board, a distinction is made in particular between plug-in and surface-mounted housings; and with regard to the connection of the chip to the external connectors of the housing, the distinction is especially between the wire-bonding and flip-chip methods.
In the course of the continually progressing miniaturization of extremely powerful electronic devices and their components, for several years miniaturized circuit housings have been constructed, the dimensions of which are only negligibly larger than those of the chips installed in the housing, and which therefore are generally designated chip-scale packages (CSP). Appreciable shares of the market have also already been gained by housings designed to be installed directly on the—still undivided—wafer, which thus are called wafer-level packages (WLP). In this case the connections are customarily made by a modified flip-chip method, in which the contact surfaces of the flip on one hand and of the housing or board on the other (the so-called pads) are connected to one another in a wireless manner, by way of soldered points (known as “bumps” or, because they usually have a nearly spherical shape, as “solder balls”).
The above-mentioned miniaturized housings, in particular the WLPs, have already been used for a considerable number of different products, in particular for serial EEPROMs, flash memory and integrated passive component configurations (IPDs), as well as analog HF and power circuitry. A beginning has also been made in packaging DRAMs with these techniques. Hence the term “circuit” in the following should be understood to mean any kind of integrated electronic component configuration that can be provided with a miniaturized housing of the kind mentioned above.
The housings of interest here are made substantially of plastic or ceramic and as a rule are hermetically sealed. Ceramic housings, after chip attachment and connection have been completed, are closed with a ceramic lid (which is pressed on) or a metal lid (which is soldered into place), and a sealing glass is used to create a tight join between lid and housing wall. To finish off a plastic housing, the still-connected chip carriers (lead frames), on which as many as 100 circuits are disposed in strips, are coated at high temperature with epoxy resin that has been loaded with minerals.
The combination in an extremely small space of such diverse materials, with widely differing thermal expansion coefficients, produces various problems with respect to reliability. Particularly stubborn problems have proved to be caused by cracks and fractures in the solder connections between the contact surfaces of chips and housing—that is, the above-mentioned bumps. Attempts have been made to increase their mechanical stability by surrounding them with a polymer “collar”, which is an extremely elaborate technical procedure. These and similar developments, however, have not been altogether successful. Furthermore, the chips themselves have proved to be at risk of breaking; in particular, microcracks have considerably endangered their long-term reliability.
The objective of the invention is thus to disclose an improved circuit housing of this generic kind that provides a substantial increase in reliability of the chip-housing unit without a serious increase in costs.